This invention relates to sewing machines and, more particularly, to a sewing machine utilizing electronic intelligence for controlling the needle thread.
In a conventional sewing machine, the only control of the needle thread is the tension applied during the setting of a stitch. This tension control typically takes the form of a pair of discs between which the thread passes on its way from the supply of thread to the eye of the thread carrying needle. In particular, the tension discs are situated between the thread supply and the take-up lever, and are forced together with an amount of force determined by the position of an operator controlled tension setting dial. This conventional tension control arrangement possesses a number of disadvantages. For example, the operator typically sets the thread tension at some value which is a compromise value for a range of stitch sizes. Also, the frictional characteristics and thickness of thread utilized effects the ultimate thread tension in the above-described type of tension control arrangement. In any event, a certain amount of experimentation, depending upon the skill of the operator, is required to adjust the thread tension in order to maintain uniform stitch quality under varying conditions.
It is therefore an object of this invention to provide an improved thread tension control system.
It is another object of this invention to reduce the skill necessary to operate the sewing machine effectively.
In a conventional sewing machine, of the type described hereinabove, the needle thread dynamics of supply and tension are controlled by the action of a take-up lever in conjunction with a check spring and a tension control arrangement of the type described above. The take-up lever is typically coupled to perform reciprocatory motion in a fixed relation to the rotation of the sewing machine armshaft, and its motion does not vary from this fixed relation. The control of the thread which can be attained through the use of such an arrangement is therefore very limited.
It is therefore a further object of this invention to provide an arrangement for controlling the take-up lever.
In particular, it is an object of this invention to provide an improved needle thread control arrangement wherein the take-up lever is independently controlled to effect thread tension control.